1. Field of the Invention
The disclosures herein generally relate to a fixing device and an image forming apparatus, and in particular relate to a fixing device that heats a heating body by an induction heating method using plural coils for induction heating.
2. Description of the Related Art
An electrophotographic image forming apparatus in the related art has a fixing device for fixing a toner on a paper. The heating methods of the fixing device include an IH (Induction Heating) method. In a power unit for induction heating (inverter), an alternate current value applied to a coil for induction heating is controlled according to an operation frequency of a switching element mounted on the inverter (conduction time width in the switching element).
Moreover, in the image forming apparatus in the related art, papers having various sizes (widths) are used according to a specification. For example, Japanese Published Patent Applications No. 2006-206813 and 2001-312178 and Japanese Patent No. 4021707 describes an image forming apparatus in which plural coils for induction heating are arranged along an axis direction of a heating roller so as to fit a width of passing paper, and an electric power supplied to the coils for induction heating is controlled.
Moreover, in the image forming apparatus in the related art, when an electric power is supplied to each of the plural coils for induction heating arranged along a direction of a roller axis, an electric energy generated by each of the coils for induction heating is changed according to a temperature difference in a longitudinal direction of the roller. In the above operation, the plural coils for induction heating are driven in frequencies different from each other, and an interference sound may be generated.
In order to inhibit the interference sound as above, it is known to perform control by switching the timing of supplying the electric power to the plural coils for induction heating. However, when the timing of supplying the electric power is switched while the distribution ratio is maintained in order to inhibit the interference sound, the plural coils for induction heating heat with time division, and a time to reach the fixing temperature becomes long.